Underwater drilling



--1 P P "a u u R. P. VINCENT 3,277,969

UNDERWATER DRILLING E6 Oct. 11, 1966 I 3 Sheets-Sheet 1 Filed Feb. 7, 1964 RENIC R VINCENT INVENTOR.

ATTORNEY.

0a. 11, 1966 P, vmcm 3,277,969

UNDERWATER DRILLING Filed Feb. 7, 1964 5 Sheets-Sheet 2 RENIC P. VINCENT 2 INVENTOR.

ATTORNEY.

Oct. 11, 1966 R. P. VINCENT UNDERWATER DRILLING Filed Feb. 7, 1964 3 Sheets-Sheet 5 RENIC P. VINCENT INVENTOR.

I WM W 1 l J l 39\ 38 V 47 38 (NORTH) (SOUTH) a a 46 e 9 38 (SOUTH). (N RTH) ATTORNEY.

United States Patent 3,277,969 UNDERWATER DRILLING Renic P. Vincent, Tulsa, Okla., assignor to Pan American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware Filed Feb. 7, 1964, Ser. No. 343,294 Claims. (Cl. 1755) This invention relates to operations in a well underlying a body of water, and more particularly it relates to drilling such wells from a floating vessel. Further, the invention is concerned with apparatus for determining the position of a floating drilling vessel located above a submerged Well and for preventing the overstressing of a tubular member extending downwardly from the vessel to the well.

In drilling submarine wells from a floating vessel, one method often employed is to anchor a drilling base having a relatively short string of surface casing attached thereto to the underwater formation and extending a conductor conduit from the vessel to the well. This conductor pipe, commonly referred to as a riser pipe, may be used to guide equipment into the well and to circulate drilling fluid between the vessel and the well. The lower end of such a riser pipe is usually fixedly connected to the surface casing through appropriate connectors, and, typically, the riser pipe is secured by cables or the like at its upper end to the vessel, with the upper end of the riser pipe extending above the water level and being located beneath a rotary table on the vessel. A drill string is normally supported by apparatus on the vessel and extends downwardly through the riser pipe, with a drilling bit at its lower end to drill a hole in the formation. Ideally, the drilling vessel is positioned directly above the well site. However, wind, current and tidal forces tend to displace the vessel from its position directly above the well, and this displacement generally occurs in spite of efforts to. anchor the vessel or otherwise maintain its desired position. The result most often is that the vessel continuously moves back and forth. Such to-and-fro motion is tolerable as long as the lateral displacement is maintained within limits, such that overstressing does not occur in the tubular members extending downwardly from the vessel to the well.

The need for preventing overstressing of the tubular elements, for example, the drill pipe, has long been recognized and various methods and devices have been proposed for indicating the position of the vessel with respect to the well and for reducing the likelihood of creating undesirable high stresses in these elements. For example, various types of orienting devices, such as inclinometers, have been proposed for use on the tubular elements to provide information as to the position of the vessel. However, the accuracy of such prior art devices has been found to be subject to error, as a result of changes in water depth, the effect of tidal currents, the effect of salt water on the system and other such factors which produce adverse effects. Further, such devices measure and indicate conditions associated with the bending of the drill pipe, for example, but are not capable of sensing the forces which are directly responsible for producing undesirable high stresses in the drill pipe.

The general object of the present invention is improved apparatus for accurately determining the deviation of a rilling vessel from a submerged well site below the vessel, and for determining stresses in an elongated element, such as a drill string, extending from a floating vessel to the submerged well. Other objects will become apparent from the following description of the invention and from the accompanying drawings.

According to the invention, the position of a floating drilling vessel and/ or the stress in a tubular member extending from the vessel to a well location in a submerged 3,277,959 Patented Oct. 11, 1966 formation below the vessel may be determined by measuring directly the force with which an element, such as a drill string, bears laterally against a fixed member, such as a conduit extending from the vessel and having its lower end maintained in a fixed position adjacent the well location. The invention is particularly useful in operations conducted in deep water, for example, where the water depth may be about feet to 600 feet or greater.

One embodiment of the invention provides apparatus of the above type comprising a floating vessel positioned above a formation underlying a deep body of water; a riser conduit extending downwardly from the vessel to the submerged well location, the conduit being connected to the vessel adjacent its upper end and anchored to the formation adjacent its lower end; anchoring means adjacent the lower end of the conduit and in contact with the formation; a flexible joint in said conduit above the anchoring means to permit the upper portion of the conduit to move laterally with the movement of the vessel; a drill string normally supported by the vessel and extending downwardly through the conduit into the bore of the well; and sensing means in the conduit between the flexible joint and the anchoring means to sense the force with which the drill string bears against the conduit when the upper end of the conduit moves laterally beyond a predetermined distance from the well location.

The present invention will be better understood by reference to the following description thereof and to the accompanying drawings of a preferred embodiment of the invention.

In these drawings, FIGURE 1 schematically illustrates a floating drilling vessel positioned over a submerged well site, together with apparatus according to the invention; and

FIGURE 2 is a vertical cross-sectional view of a spool element employed in the apparatus of FIGURE 1 and employing an electrical sensing means according to the apparatus of the invention; and

FIGURE 3 illustrates a typical electrical sensing element utilized in the invention; and

FIGURE 4 schematically illustrates an electrical system employed with the sensing element of FIGURE 3; and

FIGURE 5 is a vertical cross-sectional view of a spool element employed in the apparatus of FIGURE 1 and utilizing a hydraulic sensing means according to the invention.

Referring to the drawings, in FIGURE 1 a floating drilling vessel 11 is anchored by means of cables 12 attached to anchors (not shown) on the sea floor so that vessel 11 is positioned over a well 13 in formation 14 beneath a body of water 15. A riser pipe assembly 16 is flexibly connected by cables 17 or the like to vessel 11, and the riser pipe extends downwardly from the vessel through the water to a location adjacent the well site. Typically, surface casing 18 extends through a drilling base 19 into formation 14 to a suitable depth, and is affixed to the formation to anchor the lower end of riser pipe 16 in a fixed position adjacent the well. At its upper end, casing 18 is connected by a suitable connector 19' to double blowout preventer 21 which is equipped for remote hydraulic actuation from the drilling vessel.

Above the blowout preventers is positioned a tubular spool element 22 which forms part of the riser assembly and has mounted thereupon a sensing means 23 (as hereinafter described). Joined by connection 24 to the upper end of spool element 22 is a tubular flex-joint 26 which permits lateral movement of the upper end of the riser pipe 16 while the lower end is maintained in a fixed position. In this manner the upper end of the riser pipe 16 is free to move as the vessel is laterally displaced from its position above the well site, without damage to the lower end of the riser pipe at which the maximum bending moment occurs. The flex-joint 26 may be any of the various designs of flex-joints manufactured commercially for this purpose. Preferably, however, the flexjoint is of the cutout design (as indicated by the broken lines on the drawing) and provided with a fluid-tight, flexible rubber surface covering. Preferably, there is positioned in the riser pipe assembly above the flex-joint and near the surface of the water, a slip-joint 27 comprising an outer barrel element 27a and an inner mandrel element 27]) which slides vertically within the barrel to compensate for changes in the water depth resulting from tides and the like. Such slip-joints are well known in this art and various types are commercially available.

On board vessel 11 there is mounted the usual derrick, hoisting equipment, rotary table, rotary drive unit and other associated drilling equipment. Since these equipment items are conventional apparatus and form no part of the invention, they are not shown in the drawings and need not be further described herein. During drilling operations a string of drill pipe 28 is normally supported from the vessel and extends downwardly through rotary table 30, through rise'r pipe 16 and into the bore of well 13. A drill bit 29 is provided on the lower end of the drill string to contact formation 14 and form a hole in the formation when rotated. Typically, a drilling fluid is circulated down drill string 28, through bit 29 and up the annular space between the well bore and the drill string, and then upwardly between the drill string and the riser pipe to a mud pit located at the waters surface.

When a predetermined lateral displacement of the vessel occurs from its position above the well site, the upper end of riser pipe 16 is also displaced. The flexjoint 26 bends, while the other fixed elements of the conduit below the flex-joint, i.e., spool 22, the blowout preventer stack, etc., remain fixed. The result is that the upper end of the riser pipe 16 is free to pivot in a limited are about flex-joint 26, and the equipment below the flex joint remains in a fixed position since it is anchored to the formation. Drill string 28 within riser pipe 16 also tends to bend about the pivot, i.e., the flex-joint, and the drill string below the flex-joint moves against the inside wall of fixed spool 22 and bears laterally against the force sensing means located on the spool. In accordance with the invention, the magnitude and direction of vessel displacement are determined by relating the displacement to the force with which the inner tubular element, such as the drill pipe, bears against the riser pipe. Various means for sensing and indicating such lateral bearing force may be used and preferred alternative embodiments will be described hereinafter.

Normally, the vessel and the upper end of the riser pipe may move laterally, within a predetermined distance from a position directly above the well, without causing prohibitively high stresses in the tubular elements depending from the vessel. For example, the stress in drill string 23 will be determined by the distance from the spool element to the rotary table, the lateral displacement of the vessel, the wall thickness and diameter of the drill pipe, the tension in the drill pipe at the spool, etc. With a knowledge of such variables, the permissible displacement can be calculated by well known techniques for each situation. As shown in FIGURES 2 and 5, a suitable spacing is provided between drill pipe 28 and wear sleeve 31 when positioned vertically. Thus, for example, when vessel 11 moves to the left a preselected distance, the drill pipe 28 swings to the left to bear laterally against the sleeve 31, transmitting the lateral bearing force to sensing means 23. The lateral bearing force will be related to the magnitude of vessel displacement and the location at which the pipe bears against the sleeve will be related to the direction of displacement.

Multiple sensing elements advantageously are employed in sensing means 23 provided in spool element 22, and typically four such elements are spaced around the spool, with north, south, east and west orientations. As shown in FIGURES 2 and 5, a cylindrical wear sleeve 31 is positioned inside spool element 22. It is preferred to employ such a wear sleeve in order to reduce the wear on the spool element and to provide a suitable means for transmitting the bearing force of the pipe string to the sensing means. Advantageously, wear sleeve 31 is latched in place and may be removed by suitable tools in a manner well known in this art. The wear sleeve typically is fabricated from mild carbon steel or other suitable material.

As shown, four sensing elements 23 are spaced at equidistant intervals around the spool element 22 to contact the outside surface of wear sleeve 31 when drill pipe 28 bears laterally against the inside surface of the wear sleeve. Typically, the sensing elements are unstressed when the vessel is directly above the well and lateral displacement of the vessel beyond a predetermined distance causes the drill pipe to bear against one side of the sleeve and produce compressive stresses in the corresponding sensing elements. Typically, as shown in FIGURE 2, such sensing elements comprise a plug member 33 threaded into a boss or coupling 34 in the wall of the spool to provide a fluid-tight connection. Each sensing element further comprises an inner bearing member 36 to contact wear sleeve 31 and transmit the bearing force to a stressed member 37 on which are provided one or more electrical resistance strain gauges 38. These strain gauges may be of the wire-grid type or of the semiconductor type, such as those utilizing piezoresistive materials, for example, silicon or germanium crystals. Electrical conductors 39 connect the strain gauges into a suitable electric circuit. It is necessary to adequately Waterproof strain gauges employed in the sensing elements in order to prevent shortcircuiting and to assure accuracy of measurement, as it is well known in the art. External cover 41 is provided on the sensing element with fluid-tight seals, such as O-rings 42, to exclude moisture, dirt and the like. Typically, electrical conductors 39 are run through conduit 43, and advantageously, these are run in a single conduit 40 extending along the riser pipe to appropriate instrumentation and indicators 40a located on vessel 11.

Typically, each sensing element is provided with a pair of electrical strain gauges adhered to the surface of the stressed member 37 to measure the compressive stress in such member resulting from the lateral force applied to the stressed member when drill string 28 bears against sleeve 31. As shown in FIGURE 4, electrical conductors 39 from each of the strain gauges are connected into a bridge circuit 44 which is connected to an amplifier 46 and an indicating device 47 (or recording device, if desired) which is calibrated to indicate directly the magnitude of the deviation of the vessel from its desired position directly above the well location. Innerconnected power supply 48 provides electrical energy for operating the strain gauges adhered to the sensing element. Nor mally, it is not necessary to provide for temperature changes in the strain gauges. As shown, the two north gauges 38 (north), may be employed in the bridge with two south gauges 38 (south), completing the bridge. With such a system only two indicators, one indicating north-south orientation and the other indicating east-west orientation, are used on the apparatus. However, if temperature compensation is desired, the system may he altered in the well-known manner to provide this feature.

As shown in FIGURE 5, an alternative sensing means may be employed in lieu of the strain gauge system described above. In this latter embodiment, multiple elements are employed and each sensing element comprises a hydraulic piston 51 slidably positioned in a hydraulic cylinder 52 axially aligned in the wall of spool element 22. Hydraulic conduit 53 connects piston 52 with pres sure gauge 54, which is typically mounted on vessel 11. Conduit 53 and piston 54 are filled with a suitable hydraulic fluid, such as an oil. When the drill pipe is vertical, the pressure in the conduits is stable. However, when the vessel is displaced laterally, the drill pipe bears against sleeve 31 on the side in the direction of displacement, the hydraulic pressure in the conduits varies according to the magnitude and direction of displacement. For example, when drill pipe 28 bears against wear sleeve 31, as mentioned above, the lateral bearing force is transmitted to the appropriate piston which is driven outwardly in its cylinder so that the hydraulic fluid pressure in the conduit is increased. Such pressure variations are indicated on the corresponding pressure gauge. Preferably, each pressure gauge 54 is calibrated in terms of displacement of vessel 11 from its desired position directly above the well site. As mentioned above, four hydraulic cylinders and pistons may be spaced equally around the circumference of spool element 22 and located in the north, south, east and west positions. Then, the corresponding fcur pressure gauges on the vessel indicate the magnitude and direction of vessel displacement.

In order to calibrate pressure gauges 54 or strain gauge indicators 47 so as to have these indicators accurately display the magnitude and direction of vessel displacement, it is necessary to accurately orient the sensing elements on the riser conduit and to maintain the orientation when attaching the riser pipe assembly to the blowout preventer stack. Normally, the riser pipe assembly is made up on board vessel 11 and then lowered by suitable equipment to the well location, and the bottom connections may be made up automatically when the equipment is lowered, or a diver may be employed to assist in the connection. In either event, the orientation of the sensing elements is maintained accurately. It is necessary also to know accurately the water depth, or more correctly, the distance from the rotary table to the location of the flexjoint and spool element 22, as well as the characteristics of the drill pipe employed in drill string 28, since these factors, together with the tensile load on the drill pipe at the spool, will affect the degree to which drill string 28 .is stressed by lateral displacement of the vessel from its desired position. For this purpose, suitable charts or tables may be prepared, based on previous calculations, indicating permissible lateral displacement of the ship for existing conditions.

When, from the indicator readings, it is indicated that the vessel has moved laterally beyond a preselected distance from the desired position directly above the well site, the vessel may be relocated to correct the unwanted displacement 'by adjusting tension in the appropriate anchor cables or by propulsion of the vessel to move it in the appropriate direction until it is within a predetermined horizontal distance from the well location so that the stress in the drill pipe is maintained at a suitably low level.

The foregoing description of the present invention has been given for the purpose of exemplification. From a reading of the above description, various modifications and alterations will become apparent to the skilled artisan, and as such, these fall within the spirit and scope of the invention. For example, the sensing means may be located at a point along the riser pipe other than immediately below the flex-joint as described above, although all locations do not necessarily provide identical results. In certain instances it may be advantageous to position the sensing means either above the surface of the water, e.g., in the rotary table assembly, or at a location just below the rotary to provide an indication of the stresses in the drill pipe resulting from lateral displacement of the vessel from its position over the well. It may be found desirable to locate the sensing means in the riser pipe near its upper end. By so locating the sensing means the need for underwater connections between the sensing means and the indicators is obviated and the components are more accessible for servicing.

I claim:

1. Apparatus for conducting operations in a Well in a formation underlying a body of water, which apparatus comprises:

a floating vessel positioned above said formation,

a conduit extending downwardly from said vessel to said well, said conduit being connected to said vessel adjacent its upper end and having its lower end anchored adjacent said formation,

said conduit being flexible at a location near its lower end to permit lateral movement of the upper portion of said conduit,

an elongated element inside said conduit and adjacent the lower end thereof and extending across said flexible location to bear against said conduit when the upper portion of said conduit moves laterally, and

sensing means connected to said conduit to sense the bearing force of said conduit against said elongated element and to provide an indication of the lateral movement of said conduit.

2. Apparatus for conducting operations in a well in a formation underlying a body of water, which apparatus comprises:

a floating vessel positioned above said formation,

a conduit extending downwardly from said vessel to said well, said conduit being connected to said vessel adjacent its upper end and having its lower end anchored adjacent said formation,

a flexible joint in said conduit adjacent the lower end of said conduit to permit lateral movement of the upper portion of said conduit,

a pipe string depending from said vessel through said conduit and extending below said flexible joint so as to bear against said conduit when the upper end of said conduit moves laterally, and

sensing means below said flexible joint to sense the lateral bearing force of said conduit against said pipe string and to provide an indication of the lateral movement of said conduit.

3. Apparatus for drilling a well from a floating vessel in a formation underlying a deep body of water, which apparatus comprises:

a floating vessel positioned above said formation,

a riser conduit ext-ending downwardly from said vessel to the location of said well, said conduit being connected to said vessel adjacent its upper end and being anchored to said formation adjacent its lower end,

anchoring means in contact with said formation and adjacent the lower end of said conduit for securing the lower end of said conduit with said formation,

a flexible joint adjacent the lower end of said conduit and above said anchoring means, said flexible joint forming a portion of said conduit and permitting the upper portion of said conduit to move laterally with the movement of said vessel,

a drill string depending from said vessel through said conduit into the bore of said well,

a spool element forming a portion of said conduit and positioned between said flexible joint and said anchoring means,

sensing means on said spool element to sense the force with which said drill string bears against said spool element when the upper end of said conduit moves laterally beyond a predetermined distance from the location of said well.

4. The apparatus of claim 3 including indicating means connected to said sensing means for indicating the magnitude and direction of movement of said conduit.

5. The apparatus of claim 4 wherein said sensing means comprises a plurality of strain gauge element spaced around said spool element to sense variations in the magnitude and direction of the force with which said drill string bears against said spool element and said indicating means including means connected independently to each strain gauge element so that the direction of force is indicated.

6. The apparatus of claim 4 wherein said sensing means comprises a plurality of hydraulic cylinders and pistons spaced around said spool element, each said hydraulic cylinder being connected independently to said indicating means to sense variations in the magnitude and direction of the force with which said drill string bears against said spool element.

7; The apparatus of claim 4 including a wear element positioned in the bore of said spool element between said drill string and said sensing means, said Wear element being adapted to transmit said bearing force from said drill string to said sensing means.

8. Apparatus for conducting operations in a well in a formation underlying a body of water, which apparatus comprises a floating vessel positioned above said formation; an elongated element supported from said vessel and extending from said vessel into said well; sensing means responsive to force and surrounding said elongated element and positioned to bear against said elongated element when said vessel is laterally displaced beyond a preselected distance from a position directly above the location of said well to detect the force that said elongated element bears on said sensing means to provide an indication of the lateral displacement of said vessel.

9. In the art of marine well operations, the method of ascertaining the lateral displacement of a floating vessel from a predetermined position above a submerged well location, which method comprises:

positioning a floating vessel in a body of water overlying a submerged well location,

extending an elongated element from said vessel to said well location, positioning a sensing means having a plurality of spaced force sensing elements adjacent said elongated element and radially spaced with respect to the center of said elongated element to contact said elongated element when said vessel is laterally displaced from a position above said well location,

sensing independently the force with which said elongated element bears against each of said spaced force sensing elements of said sensing means when said lateral displacement occurs, and

employing said sensed force to ascertain the magnitude and direction of said lateral displacement.

10. An apparatus for conducting operations for drilling a well in a formation from a floating vessel using a pipe string, which apparatus comprises:

a conduit extending downwardly from said vessel to said Well and including means for connecting said conduit to said vessel and for anchoring its lower end adjacent the said formation;

a flexible joint in said conduit adjacent the lower end of said conduit to permit lateral movement of the upper portion of said conduit When the lower portion is anchored to said formation;

force measuring means below said flexible joint and having a plurality of spaced individual force measuring elements for measuring the magnitude of force exerted against each such measuring elements, said measuring means being interior of said conduit, said spaced force measuring elements being radially spaced with respect to the center of said conduit.

References Cited by the Examiner UNITED STATES PATENTS 2,299,722 10/1942 Burns et al H 73100 2,606,003 8/1952 McNeill 85 3,010,214 11/1961 Postlewaite 17545 X 3,032,105 4/1962 Reistle 166-665 3,032,125 4/1962 Hiser et al 16666.5 X 3,103,976 9/1963 De Vries et a1. 16666.5 X 3,137,348 6/1964 Ahlstone et a1. l66665 X 3,142,343 7/1964 Otteman et a1. 16666.5 X

CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner. 

1. APPARATUS FOR CONDUCTING OPERATIONS IN A WELL IN A FORMATION UNDERLYING A BODY OF WATER, WHICH APPARATUS COMPRISES: A FLOATING VESSEL POSITIONED ABOVE SAID FORMATION, A CONDUIT EXTENDING DOWNWARDLY FROM SAID VESSEL TO SAID WELL, SAID CONDUIT BEING CONNECTED TO SAID VESSEL ADJACENT ITS UPPER END AND HAVING ITS LOWER END ANCHORED ADJACENT SAID FORMATION, SAID CONDUIT BEING FLEXIBLE AT A LOCATION NEAR ITS LOWER END TO PERMIT LATERAL MOVEMENT OF THE UPPER PORTION OF SAID CONDUIT, AN ELONGATED ELEMENT INSIDE SAID CONDUIT AND ADJACENT THE LOWER END THEREOF AND EXTENDING ACROSS SAID FLEXIBLE LOCATION TO BEAR AGAINST SAID CONDUIT WHEN THE UPPER PORTION OF SAID CONDUIT MOVES LATERALLY, AND SENSING MEANS CONNECTED TO SAID CONDUIT TO SENSE THE BEARING FORCE OF SAID CONDUIT AGAINST SAID ELONGATED ELEMENT AND TO PROVIDE AN INDICATION OF THE LATERAL MOVEMENT OF SAID CONDUIT. 